1. Field of the Invention
The present invention relates to a structure of a display panel and a fabricating method of the same. More particularly, the present invention relates to a structure of an active-matrix organic electroluminescent display panel and a fabricating method of the same.
2. Description of the Related Art
Organic electroluminescent (OEL) displays are light, thin and readily portable like liquid crystal displays (LCD) are, but do not need an additional backlight source, and therefore are getting more and more attention in the market. OEL displays can be divided into active-matrix OEL displays and simple-matrix OEL displays, wherein the active-matrix ones are preferred because they emit light continuously and can be driven by lower voltages.
Among the active-matrix OEL displays, those utilizing a-Si thin film transistors (TFT) can be manufactured at lower cost, and in larger size because of the better uniformity in manufacturing processes. However, due to the low electrical conductivity of a-Si material, only N-type TFTs are formed in an active-matrix OEL display, and the design of circuit interconnection is therefore restricted. In one option, the source of a TFT is connected with the anode of an organic light-emitting diode (OLED). However, when the voltage across the TFT is shifted, the voltage on the gate electrode will affect the voltage on the source to cause an unstable current through the OLED. In another option, the drain of a TFT is connected with the cathode of an OLED, so the current through the OLED is not affected by the voltage on the drain.
The process for fabricating an OEL display element with the second option mentioned above is illustrated in FIG. 1. A TFT 110 consisting of a gate 102, a gate insulator 104, a channel layer 106, a source 108a and a drain 108b is formed on a substrate 100, and a passivation layer 112 is formed over the substrate 100. Then, a metal electrode layer 116 is formed on the passivation layer 112 as the cathode of an OLED, electrically connecting with the drain 108b through an opening 114. An electron transporting layer 118, an emitting layer 120, a hole transporting layer 122 and a hole injection layer 124 are sequentially formed on the metal electrode layer 116 to constitute an organic function layer 126 together. Thereafter, a transparent conductive layer 128 is formed on the organic function layer 126 as the anode of the OLED.
However, the OEL display element illustrated in FIG. 1 has some problems described below.
Conventionally, an OLED is formed by sequentially stacking a transparent conductive layer, a hole injection layer, an emitting layer, an electron transporting layer and a metal electrode layer, wherein the electron transporting layer usually includes Tri(8-Quinolinolato-N1O8)Aluminum (Alq3), and the metal electrode layer includes a LiF/Al composite layer. After the electron transporting layer and the metal electrode layer are formed, aluminum is usually formed on the metal electrode layer with a sputtering process. The sputtering energy is capable of driving lithium atoms from the LiF layer to the electron transporting layer, and the lithium atoms bond with the Alq3 complexes in the electron transporting layer to enhance the efficiency of electron injection.
However, when the structure illustrated in FIG. 1 is adopted in consideration of the advantage of connecting the drain of the TFT and the cathode of the OLED, the metal electrode layer is formed prior to the electron transporting layer. Therefore, lithium atoms are not driven into the electron transporting layer, and the luminescence efficiency of the OEL display panel cannot be enhanced.